The present invention relates to a device for driving a sprocket of a bicycle, which enables a rider to easily rotate two pedals thereof even with little force particularly when the cranks of the pedals are vertically positioned.
Generally, a bicycle has a larger sprocket with two pedals installed axially thereon and a smaller sprocket mounted on its rear wheel with the two sprockets being connected to each other by a chain. Its running system is that as the rider rotates the pedals, the power of the pedals is transferred to the rear wheel by the chain to get the bicycle to run.
Accordingly, if the rider steps on two pedals mounted on both sides of the larger sprocket alternately, the larger sprocket is supposed to be rotated simultaneously as the pedals are rotated.
When stepping on the said pedals alternately, the rider steps on them with ease when the cranks of the pedals are horizontally positioned. But, when the said cranks are vertically positioned, the pedals get to be positioned on the top dead center where the bending moment becomes least and consequently, the rider gets to step on the pedals in a very uncomfortable posture.
In such an uncomfortable posture, it is very difficult for the rider to use a large force so that he has much difficulty in rotating the pedals. The only way to overcome the difficulty when the cranks are vertically positioned is to use the inertial force generated as the pedals are rotated. However, in case the inertial force is not used, it is very difficult to get the bicycle to run.
The object of the present invention is to solve the above problems by providing a device for driving a sprocket of a bicycle which enables a rider to rotate two pedals thereof with ease even with a little force when the cranks of the said pedals are vertically positioned.
To achieve this object, the present invention provides a device for driving a sprocket of a bicycle, which is characterized by the system that while both cranks and both pedals are mounted on both side of an axis penetrating into the center of a sprocket of a bicycle, a circular hole is provided in the center of the sprocket so that a rotating plate with both cranks installed axially thereon may be inserted into the hole, the rotating plate supported by a cover plate fixed to the outer face of the sprocket so that it may be rotated; and further the rotating plate is supported by an elastic body so that it may be elastically rotated within a certain radius.